1. Field of the Invention
The present invention relates to low NOx producing burner apparatus and methods, and more particularly, to such apparatus and methods for separately or simultaneously burning liquid and gaseous fuels.
2. Description of the Prior Art
Because of stringent environmental emission standards adopted by government authorities and agencies, burner apparatus and methods have heretofore been developed which suppress the formation of nitrogen oxides (NOx) in flue gases produced by the combustion of fuel-air mixtures; For example, burner apparatus and methods wherein liquid or gaseous fuel is burned in less than a stoichiometric concentration of air to lower the flame temperature and thereby reduce thermal NOx have been developed. That is, staged air burner apparatus and methods have been developed wherein the liquid or gaseous fuel is burned in a deficiency of air in a first combustion zone whereby a reducing environment which suppresses NOx formation is produced, and the remaining portion of the air is introduced into a second zone downstream from the first zone wherein the unburned remaining fuel is combusted.
Staged liquid or gaseous fuel burner apparatus have also been developed wherein all of the air and some of the fuel is burned in a first zone with the remaining fuel being burned in a second downstream zone. In such staged fuel burner apparatus and methods, an excess of air in the first zone functions as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NOx.
Staged air burner apparatus and methods have most commonly been utilized for combusting liquid fuels while staged fuel burner apparatus and methods have been most commonly utilized for combusting gaseous fuels. However, burner apparatus and methods which can be selectively utilized for combusting liquid fuels or gaseous fuels or for simultaneously combusting both liquid fuels and gaseous fuels which have heretofore been developed have not met much success in reducing NOx emissions.
Thus, there are needs for improved burner apparatus and methods for separately or simultaneously burning liquid and gaseous fuel which produce flue gases having low NOx content.
By the present invention low NOx producing burner apparatus and methods for separately or simultaneously burning liquid and gaseous fuels are provided which meet the needs described above and overcome the deficiencies of the prior art. That is, in accordance with the present invention, a low NOx forming burner apparatus for burning liquid and gaseous fuels adapted to be connected to a furnace space is provided; The burner apparatus includes a housing having an open discharge end attached to the furnace space and a closed opposite end. Means for introducing a controlled quantity of air into the housing and into the furnace space are attached to the housing. A combustion compartment is disposed within the housing for providing a primary combustion zone therein having an open inlet end for receiving a portion of the air introduced into the housing as primary air and an open discharge end adjacent to the open end of the housing. The combustion compartment is smaller than the housing whereby a portion of the air introduced into the housing passes through the annular space between the exterior of the compartment and the interior of the housing and is discharged from the annular space at the discharge ends of the housing and the combustion compartment as secondary air. A liquid fuel nozzle is attached to the housing for connection to a source of liquid fuel and for discharging liquid fuel into the primary combustion zone within the combustion compartment so that the liquid fuel mixes with primary air therein, is combusted therein and is discharged into the furnace space wherein it mixes with the secondary air discharged into the furnace space and is further combusted therein. At least one primary gaseous fuel nozzle is attached to the housing for connection to a source of gaseous fuel and for discharging primary gaseous fuel into the primary combustion zone within the combustion compartment so that the gaseous fuel mixes with primary air therein, is combusted therein and is discharged into the furnace space. At least one secondary gaseous fuel nozzle is also attached to the housing for connection to a source of gaseous fuel and for discharging secondary gaseous fuel into the furnace space which mixes with the secondary air therein and is combusted therein.
The methods of the present invention basically comprise the following steps. A first portion of primary air is mixed with a liquid fuel in a primary combustion zone in a burner to form a fuel-rich mixture. The fuel-rich mixture is burned in the primary combustion zone whereby flue gases having low NOx content are formed therefrom and the flue gases and unburned liquid fuel are discharged into the furnace space. A second portion of primary air is mixed with a first portion of a gaseous fuel in the primary combustion zone in the burner and the resulting air-gaseous fuel mixture is burned in the primary combustion zone whereby flue gases having low NOx content are formed therefrom and are discharged into the furnace space. A second portion of the gaseous fuel is discharged into the furnace space and secondary air is discharged into the furnace space so that the secondary air mixes with flue gases in the furnace space, the gaseous fuel discharged therein and the unburned liquid fuel discharged therein and the resulting mixture is burned in a secondary combustion zone in the furnace space whereby additional flue gases are formed having low NOx content.
It is, therefore, a general object of the present invention to provide improved low NOx apparatus and methods for burning liquid and gaseous fuels.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.